Now would be the time to buy the combo carbon monoxide & smoke detector that is required by code to go in houses. This site will tell your state require one, Smoke and Carbon Monoxide Alarms
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lqlarryNov 26 '11 at 20:30

I just experienced the same problem. I discovered that I had installed the battery backwards. The smoke detector was chirping, so I removed battery (which was almost to hot to hold!), put another in out of same packet but in the correct orientation. No more chirping, and I have confirmed that the new battery is not overheating.